Graham Klyne [mailto:GK@ninebynine.org] wrote:
>OR:
>
>(3) use a protocol-independent way to communicate the document's URI; i.e.
>xml:base.
>
No! xml:base is not intended to communicate the document's URI. A
document's URI and a base URI are two separate concepts.
From the XMLBase spec:
[[
4.1. Relation to RFC 2396
RFC 2396 [IETF RFC 2396] provides for base URI information to be embedded
within a document. The rules for determining the base URI can be summarized
as follows (highest priority to lowest):
The base URI is embedded in the document's content.
The base URI is that of the encapsulating entity (message, document, or
none).
The base URI is the URI used to retrieve the entity.
The base URI is defined by the context of the application.
NOTE: The term "entity" in points #2 and #3 above uses the RFC 2396 meaning
of the term. Elsewhere in this document the term "entity" is used in the XML
sense.
This document specifies the details of rule #1 for embedding base URI
information in the specific case of XML documents.
]]
Hence xml:base is used to override any document URI for the resolution of
relative URIs.
Now, fragments are _not_ considered part of a URI. From RFC2396 section 4:
[[
4. URI References
The term "URI-reference" is used here to denote the common usage of a
resource identifier. A URI reference may be absolute or relative,
and may have additional information attached in the form of a
fragment identifier. However, "the URI" that results from such a
reference includes only the absolute URI after the fragment
identifier (if any) is removed and after any relative URI is resolved
to its absolute form. Although it is possible to limit the
discussion of URI syntax and semantics to that of the absolute
result, most usage of URI is within general URI references, and it is
impossible to obtain the URI from such a reference without also
parsing the fragment and resolving the relative form.
URI-reference = [ absoluteURI | relativeURI ] [ "#" fragment ]
]]
Hence '#fragment' is an empty URI (''), plus the fragment identifier.
Again from RFC section 5.2, if a URI has no scheme, authority, path or query
then it is a reference to the current document, and further processing of
the URI is terminated.
>The requirement I was imagining was not necessarily to preserve
>persistence, but to provide a way for cross-referencing between multiple
>transient subgraphs. I.e. to reference resources defined by rdf:ID from
>outside the document.
>
>#g
You could still use a protocol-independent way to communicate the URIs
associated with each transient graph, but xml:base is not it.
regards
Lee
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